1. Field of the Invention
The present invention relates in general to a method of cleaning a probe card for testing semiconductor wafers, more specifically, to a method of effectively cleaning a probe card whose probe tips have been contaminated by debris during testing.
2. Description of the Related Art
In conventional semiconductor fabrication, wafers, prior to being cut into individual chips, are tested by a probe card to evaluate if the function of the semiconductor chips thereon is normal. During testing, a plurality of probe pins of the probe card physically contact the testing pads on the wafer under test to measure the electrical properties of semiconductor devices formed on the wafer. However, after long use, the probe pin tips are usually contaminated by various metal particles and their oxides, which influences the accuracy of the testing results during testing and lowers the test quality. Thus, the probe card must be cleaned to remove the residue on the probe tips after long use.
FIG. 1 is a schematic diagram illustrating the conventional cleaning process for the probe card. As shown in FIG. 1, the cleaning process is performed using a cleaning wafer. During the period of cleaning, probe tips 3 of probe pins 1 are regularly in contact with the surface of the cleaning wafer 5 to remove accumulated residue.
FIGS. 2A, 2B, 2C and 2D are sectional views illustrating the conventional cleaning process of the probe card. First, the probe card 10 remains motionless and the cleaning wafer 5 is lifted (step S1, as shown in FIG. 2B). When the cleaning wafer 5 moves and contacts the probe tips 3 of probe card 10, sliding and polishing actions happen between the surface of the cleaning wafer 5 and the probe tips 3 due to compression, and are mainly used to remove accumulated residue (step S2, as shown in FIG. 2C). Next, the cleaning wafer 5 is lowered (step S3, as shown in FIG. 2D). Steps S1-S3 are recursively performed for several times to complete the overall cleaning process.
In the conventional cleaning process, acceleration/deceleration of the cleaning wafer 5""s approach to or departure from the probe tips 3 is about 26.7 mm/s2, a large value. In addition, the cleaning is achieved by using irregular grooves on the cleaning wafer 5, which have a width of about 10 xcexcm, as the polishing mechanism. Usually, the cleaning wafer 5 only moves in the vertical direction and is not controlled in the horizontal direction in conventional cleaning process, and the polishing effect is made by compressing and rubbing the probe tips.
The conventional cleaning process can obtain a relatively good cleaning outcome, however some types of residue, such as melted aluminum debris that usually appears black, cannot be effectively removed by the conventional cleaning process. FIGS. 3A and 3B are photographs showing the appearances of the surfaces of the probe tips before and after the conventional cleaning process. As shown in FIG. 3A, the residue region appears black and is difficult to remove. Thus, after the conventional cleaning process, the residue region still remains in FIG. 3B, which means the cleaning operation cannot completely remove contaminant formed on the probe card.
An object of the present invention is to provide a method of cleaning a probe card or the probe pins thereon for cleaning the residue regions, especially those that are hard to remove, thereby obtaining a superior cleaning and ensuring the accuracy and the quality of the test procedure performed by the probe card.
According to the object described above, the present invention provides a method of cleaning a probe card with probe pins contaminated by testing residue. A cleaning wafer is provided first and the uneven surface and the grooves thereon are used to contact and compress the surfaces of the probe pins to polish the surfaces of the probe pins. There are two kinds of cleaning operations, depending on acceleration/deceleration of driving the cleaning wafer to approach and depart from the probe card, are performed. In the first kind of cleaning operation, the cleaning wafer is driven by a smaller acceleration for a first number of times to polish the surfaces of the probe pins. The optimization of the smaller acceleration/deceleration varies with the type of residue. For example, the optimized acceleration for melted aluminum debris is about 5xcx9c6.7 mm/s2. In the second kind of cleaning operation, the cleaning wafer is driven by a larger acceleration for a second number of times to smooth the surfaces of the probe pins. The larger acceleration is about 26.7 mm/s2. In addition, the cleaning wafer is rotated by various rotation angles to obtain superior cleaning.